How can we dynamically allocate and grow an array

Question

I am working on a project, but I cannot use any existing java data structures (ie, ArraysList, trees, etc)

I can only use arrays. Therefore, I need to dynamically up

Answer 1

public class Arr {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int a[] = {1,2,3};
        //let a[] is your original array
        System.out.println(a[0] + " " + a[1] + " " + a[2]);
        int b[];
        //let b[] is your temporary array with size greater than a[]
        //I have took 5
        b = new int[5];
        //now assign all a[] values to b[]
        for(int i = 0 ; i < a.length ; i ++)
            b[i] = a[i];
        //add next index values to b
        b[3] = 4;
        b[4] = 5;
        //now assign b[] to a[]
        a = b;
        //now you can heck that size of an original array increased
        System.out.println(a[0] + " " + a[1] + " " + a[2] + " " + a[3] + " " 
    + a[4]);
    }

}

Output for the above code is:

1 2 3

1 2 3 4 5